Keeping a tree watered is the best way to ensure a long life, but it can be difficult to see the water level sometimes, which is why blogger Eric Ayars created a reminder system with an Arduino.

Using a small sensor, an Arduino Pro Mini, a relay, transformer, and an outlet box, he created a system that can detect the amount of water in the tree's tray and blink a morse code message when it's in need of water. Sure, it's probably easier to set up an alarm every couple days to remind you, but this is a clever way to ensure you'll never forget. There's no reason you wouldn't be able to apply it to any other plants you might keep in water, so it could be used year round. You can find the full guide, with schematics and code on Hardware Hacks.